Is there any evidence that the big bang actually happened?
One piece of evidence for the big bang is that there is heat radiating around the universe, known as "universal background radiation." If there had been a big bang, it would have left behind a great deal of heat, and the uniform dispersal of the radiation conforms to scientists' models of the universe. It was first discovered in the 1960s, and was studied by the so-called COBE (Cosmic Background Explorer) which was launched into space in 1989. Some of the discoveries made by the COBE actually contributed to models of development for stars, galaxies, and other structures. Other, older evidence points to the fact that the universe is expanding. This phenomenon was first discovered by Edwin Hubble, who noticed a "red shift" that could only be explained by expansion. Expansion, in turn, suggested an explosion at the beginning of the universe.